This proposal is directed toward studies of color perception with the overall goal of relating man's color perception in the natural world to laboratory studies of color vision under reduced stimulus conditions. Two broad categories of investigation using psychophysical methods are proposed: 1. The first group of studies will compare color discrimination and color appearance using asymmetric matching and stimuli specified by their cone excitation. The stimuli will appear as related colors and unrelated colors with varying spatial structure. The effects of contrast surrounds (adjacent fields) and backgrounds (distant fields) on chromatic and achromatic brightness will be measured. Bar patterns will be used to investigate the effects of spatial parameters on induction and assimilation. Spatio-temporal properties of equiluminant colors will be measured, including apparent displacement of moving chromatic bars and chromatic band movement. Patients with uniocular disease will be sought. The altered percepts of the affected eye will be mapped into the perceptual space of the normal (or relatively normal) eye. The data should reveal important differences in color perception of related and unrelated colors and indicate weaknesses in current theories of color vision. 2. A second group of studies will examine central mechanisms that mediate color and brightness in complex scenes. The experiments are designed specifically to measure changes in appearance due to relations in three-dimensional space. The studies will determine how color and brightness of a light are affected by other stimuli perceived to fall in the same or different depth plane. Perceived depth will be manipulated by varying binocular disparity. We expect this work will reveal important new non-retinal processes mediating perception in natural viewing.